One evening a few years ago, San Francisco designer Ken Fulk happened to hear at a dinner party that one of the city's finest houses was for sale. The very next morning, he dropped by, "just for a look," and in a heartbeat, he was on the phone to longtime clients with three grown children, who were on vacation. "I think I might be standing in your new house," he announced. Bronze lanterns by Bevolo flank the front steps